1. Field of the Invention
The invention relates to an image monitor apparatus such as a finder or the like which is used in a still camera, video camera, or the like.
2. Related Background Art
In recent years, in a still camera, video camera, or the like, there has been proposed a viewpoint detecting apparatus for detecting a viewpoint in a finder picture plane of an operator, for setting a range finder frame and a photometric frame to the viewpoint, and for observing an index mark which has previously been displayed in the picture plane, thereby executing a function which was made to correspond to the index mark.
FIG. 1 shows a schematic construction of an example of a finder of a video camera having a viewpoint detecting apparatus.
In the diagram, a viewpoint detection optical system 107 is provided in a rear portion of a finder 111 of a video camera VC having a finder picture plane 112. Namely, the viewpoint detection optical system 107 has a dichroic mirror 103 for transmitting a visible light and reflecting infrared rays and an eyepiece 102 which are arranged on the same axis as a 101 for irradiating an eye E of a photographer who looks in the finder in close vicinity to the eyepiece 102. The optical system 107 further has an image forming lens 104, a photoelectric converting device 105, and a viewpoint detection unit 106 which are arranged on a reflection optical axis of the dichroic mirror 103.
The finder picture plane 112 has a rectangular shape which is laterally long as shown in a front view of the viewpoint detection optical system 107 in FIG. 2B.
The photographer observes the finder picture plane 112 through the eyepiece 102 and dichroic mirror 103. An image of the eye E of the photographer irradiated by the infrared rays emitting diode 101 is reflected just beside the finder, namely, to the short side of the finder picture plane by the dichroic mirror 103 as shown in a plane view of FIG. 2A. The reflected image passes through an optical path shown by an alternate long and short dash line and is formed on the photoelectric converting device 105 by the image forming lens 104. The viewpoint detection unit 106 detects a viewpoint of the photographer on the basis of the image of the eye which was picked up by the photoelectric converting device 105. Viewpoint information is inputted to a system control unit 109. The system control unit 109 controls a lens image pickup system 108 and makes a display circuit 110 operative.
With respect to the detection of the viewpoint, the position of the center of a pupil and the position of a reflected image (cornea reflection image) of a cornea surface of the infrared rays emitting diode 101 are obtained from the image of the eye E picked up by the photoelectric converting device 105, thereby obtaining a rotational angle of the eyeball from the relation between those two positions. Coordinates on the finder picture plane are calculated by multiplying a predetermined constant to the rotational angle of the eyeball obtained.
A processing flow for detecting the viewpoint has been described in detail in JP-A-1-241511, JP-A-2-32312, and the like.
The foregoing example has the following drawbacks in case of an arrangement of the optical system in which the optical path to the photoelectric converting device is bent in the short side direction of the finder.
Since the dichroic mirror 103 has a role to reflect the image of the eye in the direction of the photoelectric converting device 105, such a role can be accomplished so long as it has a length between points (a) and (b) shown in FIG. 2A.
However, as for the optical path from the finder picture plane 112, since the optical path of the finder is located in the outside of the points (a) and (b) as shown by an alternate long and short dash line, if the plate-shaped dichroic mirror 103 has a length between the points (a) and (b), when the photographer looks in the finder, an edge of the dichroic mirror 103 is seen like a vertical line. To avoid such a phenomenon, the dichroic mirror 103 has to be set to a long length up to the outside of the optical path in the long side direction of the finder as shown in FIGS. 2A and 2B, so that there is a problem such that the viewpoint detection optical system cannot be miniaturized.